Feature sizes are in the range of a few microns up to hundreds of microns. Currently, with the ever increasing demand for smaller, higher-quality and lower-priced products from almost all fields of industry, household equipment and entertainment electronics, the development of manufacturing methods which are tailor-made for the micro systems technique with higher precision, lower cost, larger quantities, more eco-friendly to environment are extremely urgent. Investigators have looked for various methods for the manufacturing of miniature parts.
The trend for micromanufacturing is more focused on miniaturizing or down-scaling both conventional and non-conventional methods to produce microproducts. Manufacturing processes can be categorized according to the type of energy used in the process itself, such as mechanical, chemical, electrochemical, electrical and laser processes. The classification is equally applicable to micromanufacturing. For subtractive processes, there are micromechanical cutting milling, turning, grinding, polishing, etc. Punching is the process of forcing a punch through the material and into a die to create a hole in the work piece, and the most popular method for fabricating holes for mass production.
It is often an economic way of creating shaped holes in mass production. It also offers some attractive characteristics that are superior to those of other processes, for example, machining and chemical etching, considering such features as high production-rates, better material integrity, less waste, lower manufacturing costs, etc.
Therefore, micropunching is a better option for the mass-manufacture of microproducts at a reduced cost with a proper manufacturing facility attached with uniform clearance between micropunch and microdie. Also, micropunching was demonstrated in the punching of circular and noncircular holes as small as 5 microns in size. Being a mechanical process that does not involve use of chemicals, punching is environment friendly. Therefore, micropunching can be an economic and environment-friendly way of fabricating shaped micro holes in mass production.
Tool wear is an important issue in micro punching. Ploughs induced by the ultraprecise machining can be obviously detected, and some debris distribute on the surface of the micropunch.
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Moreover, the distribution of tungsten element is denser than that of both carbon element and cobalt element, which indicates the hardness of the surface of the micropunch is hard and suitable for the micro punching process. The acetone and ethyl alcohol were taken to clean the samples of the titanium sheet carefully to attain the surfaces according to the experimental requirements, and then set the sample into the microdie.
Specimens were then punched by the microprocessing machine MP50 Made in Japan with 20 pulses per minute with feedrate of 2mm. The morphology of the punched microhole in the initial period i. Some debris distribute on both sides of the microhole can be detected obviously, especially for the front side. The relevant EDX results are expressed in Figure 4. It indicates that on the front side, debris include the materials of the micropunch W, Co, C and the material of the substrate Ti. It is worth to note that the elements such as Na, Cl, S and O are also detected due to the operating contamination in the micropunching.
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Moreover, the debris distributed on the back side is sparser than that of the front side. The microtexture of the surface of the micropunch during this period is shown in Figure 5 correspondingly. Compared Figure 5 with Figure 2 , it illustrates that the wear of micropunch in the initial is distinct. The ploughs in the surface of the micropunch become flat during the punching and the tracks of the initial ploughs only distribute sporadically on some areas.
In addition, WC particles can hardly be detected. It reveals that the dominant factors of the wear loss in the initial period mainly due to Co loss and the debris distributed originally on the surface of the micropunch at the beginning as shown in Figure 2.
Profile of the punched microholes in the quasi-stable period. The morphology of the punched microhole in the quasi-stable period the punching number ranges from to is shown in Figure 6. It shows that the punched microhole is in perfect size with the qualified profile. Although there still sparsely distribute some substrate debris in the backside Figure 6B , the profile of the punched microhole is definitely superior to that of the initial period Figure 3 Figure 6.
It elucidates that owing to the effectively combined effect of tungsten carbide and cobalt during the micropunching, the punched microholes have the higher quality along with the little wear loss of micropunch. The microtexture of the micropunch in the quasi-stable period is shown in Figure 7.
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Pieces of WC particles can be detected clearly on the surface of the micropunch. Moreover, WC particles uniformly distribute on the micropunch surface. It shows that the substrate debris attach on both sides, especially in the inner of the microhole as shown in Figure 8A , which actually prevent the practical application of microhole afterwards. Moreover, with the punching process continuing, the micropunch seriously wears.
Consequently, the substrate Ti cannot be successfully punched and sticks to the edge of the microhole. In the meantime, with the effect of punching number increment, the unsuccessful removed substrate i. In addition, a large amount of micropunch materials are peeled off and adhered to Ti substrate in this intensively severe period as shown in Figure 9.
Figure 10 shows the relevant microtexture of the micropunch in the severe period. It shows that a lot of WC particles distribute on the one side of the micropunch surface and the dominant factor of the wear loss in the severe period mainly relies on WC. Figure 12 shows the relevant results each for 5times of the diameters of the punched microholes in the micropunching of both front side and back side. The wear loss of the punched microhole at various punching period is shown in Figure It shows that the wear loss of the micropunch in the various periods is distinctive and the diameter of the punched microholes varies correspondingly.
Also, the wear loss of the micropunches is consistent with the diameter variation of the microholes. Obvious decrease of the wear loss of the micropunch in the initial period is definitely detected with the apparent change of the diameter of the microhole. Interestingly, the attractive results of the variation of the diameter of the microhole are detected when the punching number ranges from to In this period, the diameter of microhole is relatively kept stable due to the un-variation of the micropunch which indicates by the near zero weight loss of the micropunch in the quasistable period.
While the micropunching increases further i. Meanwhile, the wear loss of the micropunches increases remarkably as a result of the serious loss of cobalt.
Due to the lack of cobalt which is taken as the bonding material with tungsten carbides , the tungsten carbides are easily peeled off. As a result, the diameter of the microholes and the wear loss of the micropunches vary seriously in the severe period of micropunching.
Furthermore, with the micropunching process going further, due to the friction between the sample and the micropunch, the temperature of the micropunch will increase. Consequently, the particles of tungsten carbides are more easily peeled off due to the different thermal expansion coefficients of WC and Co. As a result, the wear loss of the micropunch is more intensive in the severe period. Moreover, if the feedrate of the micropunching increases, the more drastic wear loss of the micropunch will appear.
It should be noted that although the micropunch is in the so-called severe period, the diameter of the punched microhole is still stable to some degree, especially for the punching number between and , as shown in Figure 12 highlighted with purple dash line. However, the wear of the micropunch in this period starts to increase obviously with the tiny weight loss as shown in Figure 13 highlighted with yellow dash line.
The morphology of the relevant punched microhole during this period is shown in Figure It shows that even though the back side of the microhole is comparatively clean, the quality of the punched microhole has already deteriorated with the debris distributed in both outer and inner microhole, especially for the front side as shown in Figure Moreover, the diameter of the front side of the punched microhole is almost same as that of the back side even in the severe period as shown in Figure It indicates the punched microhole can be used directly without any post treatments.
Basudeb Bhattacharyya - Publications
This captivating result definitely pinpoints the outstanding contribution of the micropunch on the fabrication of the near-net shape microholes to meet the challenges in micro manufacturing field, especially for the bioapplications. When the punching process in the severe period Punching number exceeds , the size of micropunch are unstable due to the distinct wear loss both of Co and WC of micropunch resulted in the punched microholes with the lower quality.
The interesting unique characteristics of the micropunching is the diameter of the front side of the punched microhole is almost same as that of the back side even in the severe period, which implies the punched microhole can be used directly without any post treatments appealing to meet the challenges in micro manufacturing field related to the bioapplications.
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